How can I create a single image texture from several different, overlapping image textures?
I would create low res versions of the image textures, then bring them all into Blender and apply them to the object material with the various UV maps. (If you bake out the combined low res image you'll have a starting point for after the next step when you have all your high res texture bakes.)

Then bring in the high res image textures (one at a time) and bake out the high res UV texture as applied to the image.

Once you've baked out all the applied high res textures, you should be able to combine them all in an external image editor (alphas included if baked out properly). You can use the previous combined low res bake as a reference.

Then you'll have a single high res image texture. If Blender still cannot handle working with this single high res texture image, you'll have to lower the resolution until Blender can work with it. It should be fine on shots that are not too close to the object in your scene.